Hollow-weave airbags are used for purposes such as absorbing impacts by being caused to deploy through air being fed instantly into a bag portion structure and maintaining that deployed state for a predetermined period of time.
In recent years, these hollow-weave airbags have been used in various applications. For example, hollow weave airbags are used in life jackets, life boats, mats, home elevators, and have been installed in vehicles where, by deploying when a vehicular collision occurs, they are used as airbags that protect the head and chest portions of vehicle occupants.
In addition, one of the most important requirements for this kind of hollow-weave airbag is that a bag portion of the airbag should have excellent airtightness, such that it is able to deploy and maintain an inflated state. Furthermore, in recent years, many of the airbags that are installed in vehicles have been provided at vehicle pillars and seat sides, in order to protect the side of the head of a vehicle operator in the event of a roll-over or an impact from the side. It is necessary that this type of airbag secures the deployed state for a certain period of time in order to protect the head of a vehicle occupant, not only at the point of impact but also during the roll-over or the like afterwards. In recent years, therefore, it has been highly important for hollow-weave airbags to possess not only excellent airtightness, but also be able to secure the deployed state for the certain period of time, and be compactly storable to enable provision in the pillars or seat sides of the vehicle.
Depending on the structure, however, some hollow-weave airbags are likely to cause stitches at a boundary of the bag portion and a closed portion to open on deployment of the airbag due to air pressure inside the airbag. If this opening of stitches occurs on deployment, airtightness decreases, causing strength insufficiencies at the boundary portion or gas leaks. As a result, it may become difficult to maintain the airbag in the deployed state for a certain period of time or more.
Various airbags have been developed in order to solve this problem. For example, in Japanese Patent Laid-Open Publication No. 2000-229550, a hollow-weave airbag is disclosed that is formed with a triple weave portion and a quadruple weave portion, which have a yarn density ratio lower than a circumferential edge portion, in a peripheral area that includes a boundary of the bag portion and the closed portion, and where a coating layer is formed not only on a front face side, but also on a back face side by using a coating agent that permeates to the back side. Furthermore, in Japanese Patent Laid-Open Publication No. 2001-233153, a hollow-weave airbag is disclosed that has a 3/n basket weave structure (n is an integer of 2 or more) of only one warp yarn at the boundary of the bag portion and the closed portion on a single-layered structure. The single-layered structure other than the boundary of the bag portion and the closed portion has a 3/n basket weave structure (n is an integer of 2 or more) that has n warp yarns in a continuous fashion with the boundary portion, and a cover factor on the single-layered structure of 4,000 or more.
Although the hollow-weave airbags disclosed in both Japanese Patent Laid-Open Publication No. 2000-229550 and Japanese Patent Laid-Open Publication No. 2001-233153 possess airtightness superior to conventional hollow-weave airbags, however, it is necessary to carry out a separate coating process in order to form a coating layer in the former hollow-weave airbag, which makes the manufacturing process complicated and is also likely to increase costs. Furthermore, if the coating layer becomes too thick, folding up the airbag compactly may become difficult. On the other hand, although the latter hollow-weave airbag has superior airtightness, densifying the weave structure at the boundary in order to prevent opening of stitches at the boundary of the bag portion and the closed portion expands the boundary and makes the coating layer susceptible to non-uniformity, and as a result, compact folding may become difficult. Furthermore, although it is preferable that the weave structure of the boundary of the hollow-weave airbag be of a curved-line structure rather than a straight-line structure, in order to increase freedom of design as well as so that gas pressure is suitably dispersed rather than stress being concentrated, no mention is made in the above laid-open publications of how to maintain airtightness in the event that the weave structure at the boundaries is given the curved-line structure.